Usually the earth associated with the fuel gauge is at the tank end and connected to one leg of the sender, if not independently then via the sender mounting. In the latter case there will be an earth connection from tank to chassis to check.
Richard
2018 Roadster 3.7 1966 Land Rover S2a 88 2024 Royal Enfield Guerrilla 450 1945 Guzzi Airone
